A transcranial magnetic stimulation is a technique of stimulating neurons by inducing an eddy current in the brain through electromagnetic induction. In this technique, as shown in FIGS. 1 and 2, an alternating-current or predetermined current waveform is applied to a stimulation coil placed on the skin of the head to form a variable magnetic field and to induce an eddy current in the direction opposite to the coil current in the brain under the effect of the variable magnetic field, and an action potential is generated by stimulating the neurons with the eddy current.
The transcranial magnetic stimulation is used in clinical examinations and neuroscience including measurement of nerve conduction velocity.
In recent years, magnetic stimulation is gathering attention as therapeutic application to neuropathic pain, Parkinson's disease, depression, etc. A drug therapy may not effective to these diseases in some cases and methods of treatment in such a case include applying an electrical stimulation to the brain by implanting an electrode into the brain. However, this method of treatment requires a craniotomy and is therefore often not desired by patients.
Thus, a repetitive transcranial magnetic stimulation performed by repeatedly applying a non-invasive magnetic stimulation not requiring a surgical operation is being studied as a method of treatment. For example, it is reported that a pain-relieving effect to intractable neuropathic pain is produced for about one day after magnetic stimulation to the primary motor cortex.
However, a conventional magnetic stimulation device weighs about 70 Kg and is available only in well-equipped medical institutions because electrical work is required for installation. Additionally, since a stimulation position is determined while referring to patient's MRI data during actual treatment, the treatment must be performed by a skilled health-care professional. In the treatment of intractable neuropathic pain, a coil must be positioned on the target primary motor cortex with accuracy of 1 mm.